1. Field of the Invention
The present invention relates to a broken piece detecting sensor assembly for detecting the presence of broken piece admixed into a liquid such as, for example, a lubricant oil.
2. Description of the Prior Art
Hitherto, as a device for detecting the admixture of metallic particles or powdery metal, resulting from frictional wear and/or breakage of, for example, a combustion engine, a transmission and/or bearing assemblies, into the lubricant oil used in automotive vehicles, aircrafts or helicopters, the metallic broken piece detecting device generally called as a metal check sensor, an oil check sensor or a broken piece sensor has been suggested. (See the Japanese Laid-open Patent Publications No. S55-052943, No. S61-253455 and No. 2000-321248, and the Japanese Patents No. 2703502 and No. 2865857.) Such metallic broken piece detecting device is utilized as a mean for inspecting the soundness of various equipments such as, for example, a combustion engine, a gear box and/or bearing assemblies and is capable of providing information concerning deterioration taking place at various sites of the device to be inspected before any destructive trouble occurs at such sites.
Particularly in aircraft jet engines, downsizing and increased speed orientation thereof are currently desired for. While a spindle bearing assembly hitherto employed in the aircraft jet engine makes use of bearing rolling elements made of a metallic material, the currently utilized material for the bearing rolling elements has now come to a deadlock in promoting the increased speed orientation. In order for the material for the bearing rolling element to accommodate the high speed orientation, it is necessary for the rolling elements of the bearing assembly to be made in the form of ceramic balls or ceramic rollers made of, for example, silicon nitride (Si3N4). Also, where the ceramic balls or the ceramic rollers are employed in the bearing assembly for the jet engine, the performance is likely to be increased considerably, accompanied by increase of the efficiency of the jet engine to such an extent that the environmental loading can be reduced. On the other hand, with the conventional metallic broken piece detecting device, only broken remains of metallic material, magnetic material or electroconductive material can be detected, but it is incapable of detecting broken remains of ceramic material that is characteristically non-metallic, non-magnetic and non-electric conductive. Accordingly, in the case of the bearing assembly in which the ceramics, for example, are employed as material for the bearing rolling elements, no information concerning deterioration taking place in the bearing rolling elements before occurrence of any destructive trouble can be made available from the metallic broken piece detecting device. For this reason, bearing assemblies of such a structure are currently utilized only in aircrafts having a limited application.